This invention relates to high performance data cables that successfully enables transmission in the frequency range of 0.3 MHz to 1200 MHz and especially in the range of 1.0 to 600 MHz and/or 1.0 to 1000 MHz. Also to UL 910 high-performance plenum cables that have a non-fluorinated jacket. More particularly, the invention relates to high-performance data cable which are bound-lateral shielded twisted pair cables. Also, this relates more particularly to the at least category 5 plenum UL 910 cables having a non-fluorinated jacket and a heat-resistant flame-retardant tape on the inner circumference of the jacket.
The current high performance data cables usually utilize as a shield a heavy, stiff, 2 mil aluminum tape with a 1 mil polyester (Mylar) backing. The shield is wrapped around each unshielded twisted pair subgroup within an application lay length that is equal to the length of the cables overall cable lay, typically lays of 4.0 to 6.0 inches. The tape is about 0.5 inches wide. The application angle of the wrapping is shallow, based on the long overall cable lay (5 inches) and the tape is almost parallel with the twisted pair laterally axis. A typical cable has 4 pairs of twisted pair cables with a 40 to 65% tinned copper. braid applied over the four pairs and a final thermoplastic jacket extruded over the braided pairs to complete the cable. The shallow application angle of the metal shield tape generally creates the problem of allowing the tape to open up during the cabling operation before a binder or spirally applied drain wire can capture it.
Also, the tape doesn""t generally follow the pairs contour under the tape. Tape gaps are created with this process around the unshielded twisted pair core that do not provide a sufficiently stable ground plane to meet the industry standard electrical requirements such as CENELEC pr EN 50288-4-1.
The known cable structure noted above is mechanically unsound in a static state, and the electricals are unstable under installation conditions since the single overall braid cannot adequately insure the tape lap doesn""t xe2x80x9cflowerxe2x80x9d open when the cable is flexed. This xe2x80x9cfloweringxe2x80x9d increases NEXT, and further erodes impedance/RL performance as the ground plane is upset. This adds to attenuation non-uniformity. The impedance numbers are even worse under flexing since the conductor""s center to center, as well as the ground plane, changes. The higher the bandwidth requirement, the worse these issues become.
We know of no cable structure for high performance UL 910 plenum data cables that have a non-fluorinated jacket. A plenum cable that used a fluorinated jacket and a temperature-resistant flame-retardant separator tape such as Nomex(copyright) (a temperature-resistant flame-retardant nylon manufactured by DuPont) was used and sold by Belden Wire and Cable Company more than a year prior to this invention. The Nomex(copyright) tape in those cables kept the fluorinated (FEP) jacket from dripping and producing high peak smoke numbers in the UL 910 burn test.
Our invention uses on each twisted pair cable a lateral wrapped shielding tape that is bound with a fabric or metal binder to meet impedance/RL, attenuation uniformity, and capacitance unbalance that is required.
Our invention eliminates most of the trapped air that is normally found in shielded twisted pair cables. This is done by utilizing a lateral wrapped shield with preferably a minimum 10% overlap and which has a 0.33 to 2.0 mil and preferably a 1 mil metal layer. The lateral wrapped shield is held together by an appropriate binder and preferably by a textile or metal braid or textile helically wrapped thread to provide good shielding with improved impedance control. When desired, a short fold can be applied along the lateral seam of the shield for improved EMI/Rfi isolation. The consistent ground plane created along the cables length allows better capacitance unbalance as well as improved attenuation uniformity through the reduction of RL reflections and capacitance unbalance.
Our invention also provides for substantial geometric stability under flexing. The use of a tight lateral shield with at least a 10% overlap and a textile or metal binder, eliminates tape gaps and flowering under flexing. This establishes a very stable level of physical and electrical performance under adverse use conditions. Our twisted pair cable center to center distances indicated as (d) in FIG. 3, and conductor to ground distances, remain much more stable than those of the previous cables.
Our cables are especially beneficial for use as category 7 and higher performance cables. This is especially true for those cables that we laterally shield and bind and are used out to 600 MHz or 1000 MHz. The typical high-performance data cable when made according to our invention, has four (4) twisted pair cables with each twisted pair cable made up of two foam or non-foam insulated (fluorocopolymer or polyolefin) singles. Each of the twisted pair cables has the unique tight lateral metal shield tape wrapped around it with the tape and its lateral short fold seam tightly held in place with a tight binder such as a fabric or metal braid or a helical thread. When a braid is used as the binder, it is a 40 to 95% braid. When a thread is used, it is preferably helically wound. The bound-lateral shielded pairs are S-Z""d or planetary together into a bunched or bundled configuration. The bundled pairs may be bundled by an overall 40 to 95% braid or thread. A final thermoplastic jacket (fluorocopolymer or a polyolefin or polyvinyl chloride) is extruded over the bundled twisted pair cables.
Generally the metal shield is an aluminum tape or a composite tape such as a short fold BELDFOIL tape (this is a shield in which metal foil or coating is applied to one side of a supporting plastic film), or a DUOFOIL tape (this is a shield in which the metallic foil or coating is applied to both sides of a supporting plastic film) or a free edge BELDFOIL tape. The overall metal thickness is 0.33 to 2.0 mil aluminum layer thickness and preferably about a 1.0 mil. Although aluminum is referred to, any suitable metal normally used for such metal and composite metal tapes can be used such as copper, copper alloy, silver, nickel, etc. Each twisted pair is wrapped with the metal facing outwardly and although the most preferred wrap is about a 25% overlap, the overlap may vary as a practical matter from 10 to 50%. The preferred shield that gives the best attenuation and impedance characteristics are those tapes that are joined to provide a shorting effect. However, with a suitable overlap, the short fold can be eliminated.
The number of shielded twisted pairs in a high performance data cable is generally from 4 to 8 but may be more if desired. The tension of the laterally wrapped shield and the binder are such that the wrapped shield and binder eliminate most of the air to provide a standard impedance deviation for the bound-laterally shielded twisted pair cable and an average standard impedance deviation for the high performance data cable which has a plurality of laterally shielded twisted pairs. The tension on the shielding tape and binder are such that there is only a 25% or less and preferably 18% or less void space of the entire cross-sectional area of the laterally shielded twisted pair taken along any point in the length of the cable.
We provide a high performance twisted pair data cable having a shield laterally wrapped around an unshielded twisted pair cable and a fabric or metal braid or yarn simultaneously or subsequently wrapped around the lateral shield to bind the shield. The wrapping of the shield and binder(the braid or thread) is at a tension such that for an individual twisted pair that may be used on its own, the individual pair has an unfitted impedance that has a nominal or standard impedance deviation for each bound-laterally shielded twisted pair cable that is rated for up to 600 MHz a standard impedance deviation of 3.5 or less from 1.0 to 600 MHz and with no single impedance deviation being greater than 6.0, and for a cable rated for up to 1000 MHz a standard impedance deviation 4.5 or less from 1.0-1000 MHz and with no single impedance deviation being greater than 6.0. The high-performance data cable which has a plurality of bound-laterally shielded twisted pair cables and is rated at up to 600 MHz has an average standard impedance deviation for all of the plurality of bound-shielded twisted of pairs of 3.5 or less from 1.0 to 600 MHz and with no single standard deviation for any of the cables being greater than 6.0. The high-performance data cable which has a plurality of bound-laterally shielded twisted pair cables and is rated at up to 1000 MHz has an average standard impedance deviation for all of the plurality of bound-laterally shielded twisted pairs of and 4.5 or less from 1.0-1000 MHz and with no single standard deviation for any of the cables being greater than 6.0. The standard impedance deviation is calculated around a mean or average impedance of 50 to 200 ohms and with at least 350 frequency measurement taken on a 328 ft. or longer cable.
Also, we provide a high performance data cable that has the ability to be labeled as a UL910 high performance data plenum cable. This cable preferably has a non-fluorinated jacket and a temperature-resistant flame-retardant separator tape beneath and in contact with the jacket.